1. Field of the Invention
The present invention relates to a full text search system applying a character string collation method which searches a large quantity of data for a short time using a plurality of search processing apparatuses. What is called a character string collation method here stands for a method for examining whether a dedicated character string exists in the text data of search target while collating the dedicated character strings with the text data of search target one after another in the backward direction from the top of the text data of search target.
2. Description of the Related Art
Presented in Kokai (unexamined patent publication) No. 8-137734 titled “Information Processing System and Database Distribution Method” as prior art is a method of shortening a search time using a plurality of search processing apparatuses, wherein small-scale information processing devices such as a personal computer are connected with a personal computer LAN; data is distributed in such a way that a database for each information processing device can be almost even; the data is processed in parallel by each information processing device when the data is processed; and the processed results are integrated and displayed in one information processing device (hereinafter referred to as first prior art).
Also, there was a method of conducting search processing wherein search target data is divided into a plurality of fields; each divided field is allocated to each individual search processing apparatus; and the individual search processing apparatuses conduct search processing in parallel simultaneously. For example, presented in Kokai (unexamined patent publication) No. 9-134364 titled “Information Search System” is the following method of conducting search processing. The Information Search System comprises a plurality of search servers which perform search processing and a search management server which manages the operation of these search servers. The search management server is divided into a text base of search target (text type database), and relevant information about this text base is also divided. A combination of the divided portions of this test base and relevant information corresponding to the divided portions is allocated to part or the whole of a plurality of search servers. A plurality of search servers execute information search for the divided portion of the text base allocated by the search management server in parallel and independently. By constituting the System in such away, no special hardware is required even when a plurality of text bases are searched at the same time, and information search can be promptly done without being affected by the size of the text base of search target, thus making it possible to conduct search processing in parallel and simultaneously (hereinafter referred to as second prior art).
In the first prior art, when each divided database (when the database is divided) is made into an physically independent file for each search processing apparatus, a physical re-division of the search target data is needed if a problem of increase or decrease in the number of search processing apparatuses occurs due to an additional installation of search processing apparatuses and the breakdown of search processing apparatuses, and as a result the time duration during which the operation of the System is suspended becomes longer because of the work required for the physical re-division of the data of search target.
In the second prior art, the whole of the text type file must be rewritten when data is added or part of the data is changed, and if the file is a huge one, it takes a long time to rewrite the file. Consequently, the full text search system using the character string collation method in which search processing and data addition and update processing are carried out in parallel cannot be a practical method unless this problem of the time required for rewriting is solved. Furthermore, since a number of search processing apparatuses are used, there is a high possibility that any defect occurs to any of the search processing apparatuses.